Federal Funds Sold and Securities Financing Activities Netting of Financial Instruments - Repurchase Agreements (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2019	Dec. 31, 2018
Assets Sold under Agreements to Repurchase [Line Items]
Document Period End Date		Jun. 30, 2019
Carrying Value of Securities Purchased under Agreements to Resell and Deposits Paid for Securities Borrowed		$ 1,244	$ 1,637
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell, Fair Value Disclosure	[1]	1,244	1,637
Securities Purchased under Agreements to Resell, Fair Value of Collateral		1,228	1,624
Securities Purchased under Agreements to Resell, Not Subject to Master Netting Arrangement		16	13
Securities Borrowed or Purchased Under Agreements to Resell, Amount Not Offset Against Collateral		0	0
Securities Sold under Agreements to Repurchase, Gross		1,814	1,774
Securities Sold under Agreements to Repurchase		1,814	1,774
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities		1,814	1,774
Securities Sold under Agreements to Repurchase, Not Subject to Master Netting Arrangement		0	0
Securities Sold Under Agreements to Repurchase, Amount Not Offset Against Collateral		0	0
Federal Funds Sold		$ 7	$ 42

[1] Excludes $7 million and $42 million of Fed Funds sold, which are not subject to a master netting agreement at June 30, 2019 and December 31, 2018, respectively.